This invention is related in general to optical filters, and more particularly to optical filters which are configurable and can be used as displays.
Optical filters find widespread utility in such diverse applications as sunglasses, scientific instruments, optical communication systems, and optical data processing. Optical filters may comprise diffraction or reflection gratings. A diffraction grating would be characterized as a transmissive filter, while a reflection grating would be characterized as a reflective filter. A distributed Bragg reflector is another type of filter which can be used as a transmissive or reflective filter. A distributed Bragg reflector comprises alternating layers of transparent material wherein the alternating layers have different indices of refraction with respect to each other. A partially reflective surface exists at the interface between each layer due to the difference in index of refraction. Each layer of a distributed Bragg reflector has a predetermined thickness such that light reflected from each of the reflective surfaces interferes constructively for a narrow band of light wavelengths. Wavelengths outside of the narrow band are transmitted through the transparent layers.
An optical display can be formed using an optical filter which can be tuned, or configured. By tuning the filter element a light signal can be controllably transmitted or not transmitted to a receiver or viewer. Liquid crystal displays (LCDs) are an example of an optical filter which can be used as a reflective or transmissive display. In their simplest form, LCDs can be switched between opaque and transmissive using an electric signal. Likewise, any optical filter which can be switched between opaque and transmissive can be used as a display element. Preferably, if the filter element can be used to select between a narrow band of wavelengths of reflection rather than being merely turned on and off it can be used as a color display.
A tunable and configurable optical filter can be used in optical communication systems and optical data processing systems. A single filter which can be tuned to a particular light wavelength can separate out a number of separate data signals traveling along a single fiber optic transmission line, for example. Other uses for a tunable optical filter are readily apparent.
Until now switchable, or configurable, filter elements have been formed on rigid, inflexible substrates. Although filter elements are known which can be formed in flexible materials, these filter elements have not been configurable and so are of little use as displays or in communication and computation equipment. Further, LCDs require relatively expensive materials and processing techniques, particularly when a color display is desired.
Another important feature of a configurable filter is that it uses relatively low power so that it can be used in applications such as portable computers, automobiles, and military equipment. State-of-the-art LCDs are relatively low power, but further improvement is desirable.
Accordingly, it is an object of the present invention to provide a configurable display which can switch multiple colors of light.
Another object of the present invention is to provide an optical display which is flexible.
A further object of the present invention is to provide a reflective display which uses low power.
Another object of the present invention is to provide a tunable optical filter for optical communication use.
A further object of the present invention is to provide a tunable and configurable optical filter for optical data processing.
Still another object of the present invention is to provide a configurable display which can be manufactured at low cost using simple manufacturing methods and low cost materials.